The present invention relates generally to kiln systems and, more particularly, to the introducing of heated air into a kiln chamber for drying lumber.
Lumber which has recently been cut contains a relatively large percentage of water and is referred to as green lumber. Prior to being used in applications that demand good grades of lumber, the green lumber must be dried. Drying removes a large amount of water from the lumber and significantly reduces the potential for the lumber to become warped or cracked. Although lumber may be dried in the ambient air, kiln drying accelerates and provides increased control over the drying process.
FIG. 1 illustrates aspects of one type of conventional kiln system 20. The conventional kiln system 20 includes a kiln chamber 22 that receives a charge of lumber. The charge of lumber typically consists of two or more rectangular stacks of lumber 24. The kiln chamber 22 is a generally rectangular building that can be at least partially sealed to control the amount of air that is introduced to and exhausted from the kiln chamber. Hot air from a furnace 26 is forced through an inlet duct 28 to a plenum 30 that is positioned in an upper portion of the kiln chamber 22. The hot air is discharged from the plenum 30 to the interior of the kiln chamber 22 through multiple outlets 32 defined in the top panel of the plenum. Only a few of the outlets 32 are identified by their reference numeral in FIG. 1. The heated air supplied to the interior of the kiln chamber 22 is circulated by reversible fans 34 so that the heated air flows along a recirculating flow path that extends through the charge of lumber, during which time the air dries the lumber. The furnace 26 draws air from the interior of the kiln chamber 22 via a return duct system (not shown).
Whereas conventional kiln systems 20 of the type illustrated in FIG. 1 are functional, they operate at least somewhat inefficiently. For example, the momentum of the flow along the recirculating flow path is inefficiently sacrificed in order to accelerate the heated air discharged from the outlets 32 of the plenum 30. As another example, the heated air discharged from the outlets 32 of the plenum 30 is contemporaneously supplied to both the high and low pressure sides of the fans 34. Since the heated air has a higher specific volume than cooler air, the introduction of heated air on the low pressure side of the fans means that the fans must disadvantageously pass air having a relatively high specific volume, which is inherently less efficient than passing air having a lower specific volume. In addition, it is common in some conventional kiln systems for the heated air introduced into the kiln chamber not to mix well with the air flowing along the recirculating flow path, which can result in uneven and therefore inefficient drying of lumber.
Inefficiencies in kiln systems reduce the speed at which a charge of lumber can be dried, which can be disadvantageous since mill production depends upon the ability to dry lumber at a sufficient rate so that production need not be slowed to allow for the drying process. Inefficiencies in kiln systems also add to the cost of producing quality lumber. Of course it is advantageous to lower the cost of producing quality lumber. Whereas some conventional kiln systems can be characterized as being efficiently operated and able to dry lumber at a sufficient rate, there is always a demand for new kiln systems and kiln-related structures and methods that can be even more efficiently operated, and that facilitate the drying of lumber at a sufficient rate.
The present invention solves the above and other problems by providing improved structures and methods for introducing heated air into a kiln chamber.
In accordance with one aspect of the present invention, a kiln system includes a kiln chamber defining a chamber interior space, one or more air moving devices capable of circulating air in the chamber interior space along a recirculating flow path, a furnace capable of providing heated air, and a plenum positioned in the kiln chamber and generally separating the chamber interior space into upper and lower portions. The upper portion of the chamber interior space is positioned above the plenum, and the lower portion of the chamber interior space is positioned below the plenum and is for receiving a charge of lumber for drying. The plenum defines a plenum cavity for receiving the heated air from the furnace. The kiln system further includes one or more upright passageways that are operative for efficiently supplying the heated air from the plenum cavity to the upper portion of the chamber interior space. More specifically, each upright passageway is mounted to the plenum and in communication with the plenum cavity so that the upright passageway is capable of receiving heated air from the plenum cavity. Each upright passageway extends into the upper portion of the chamber interior space and includes at least one outlet positioned proximate the recirculating flow path in the upper portion of the chamber interior space. As a result, each upright passageway is capable of providing heated air from the plenum to the recirculating flow path in the upper portion of the chamber interior space via its outlet.
In accordance with one aspect of the present invention, the air moving devices are positioned in the upper portion of the chamber interior space and include impellers defining rotational axes. Preferably the outlets of the upright passageways are proximate hubs of the nearest respective impellers, which advantageously promotes mixing of the heated air discharged by the upright passageways.
In accordance with one aspect of the present invention, the upright passageways are constructed, arranged and operated so that the heated air discharged thereby is introduced proximate the flows being discharged by the air moving devices and in at least generally the same direction as the flows being discharged by the air moving devices. Preferably the heated air is discharged by the upright passageways at a speed that is at least approximately as great as the speed of the flow being discharged by the air moving devices. As a result and advantageously, the momentum of the flow along the recirculating flow path is not sacrificed in order to accelerate the heated air supplied to the chamber interior space by the upright passageways. Most preferably the heated air is discharged from the upright passageways at a speed that is substantially greater than the speed of the flow being discharged by the air moving devices, which advantageously enhances the flow through the air moving devices. In addition, the upright passageways are proximate the air moving devices so that the flow from the outlets advantageously reduces the pressure near the exits of the air moving devices by means of Bernoulli""s principle, which also enhances the flow through the air moving devices.
In accordance with one aspect of the present invention, each upright passageway is constructed and arranged so as to minimize its contribution to the resistance to flow along the recirculating flow path. For each upright passageway, a first cross-dimension is generally perpendicular to the length of the upright passageway and parallel to the portion of the flow path into which the upright passageway extends, and a second cross-dimension is generally perpendicular to both the length of the upright passageway and the portion of the flow path into which the upright passageway extends. The second cross-dimension is less than the first cross-dimension, whereby the upright passageway advantageously defines a low profile with respect to the portion of the recirculating flow path into which the upright passageway extends.
In accordance with one aspect of the present invention, each air moving device is capable of operating in clockwise and counterclockwise modes. Flow along the recirculating flow path travels clockwise while the air moving devices operate in the clockwise mode. In contrast, flow along the recirculating flow path travels counterclockwise while the air moving devices operate in the counterclockwise mode. Each air moving device has opposite first and second sides. The first and second sides are respectively high and low-pressure sides during the clockwise mode. In contrast, the first and second sides are respectively low and high-pressure sides during the counterclockwise mode. A first group of the upright passageways is positioned so that the outlets thereof are proximate yet preferably facing away from the first sides of respective air moving devices. In contrast, a second group of the upright passageways is positioned so that the outlets thereof are proximate yet facing away from the second sides of respective air moving devices. The kiln system includes a control system that is operative so that the outlets of the first group of upright passageway are open and the outlets of the second group of upright passageways are closed while the air moving devices operate in the clockwise mode. In contrast, the control system is also operative so that the outlets of the first group of upright passageway are closed and the outlets of the second group of upright passageways are open while the air moving devices operate in the counterclockwise mode. As a result, heated air originating from the furnace and having a relatively high specific volume is advantageously introduced substantially solely at the high-pressure sides of the air moving devices, which is inherently more efficient than having the air moving devices pass the heated air having the relatively high specific volume.
In accordance with another aspect of the present invention, each upright passageway includes both an inboard outlet and an outboard outlet. For each upright passageway, the inboard outlet is oriented toward the respective air moving device and the outboard outlet is oriented away from the respective air moving device. In accordance with this aspect, the control system is operative so that the outboard outlets of the first group of upright passageways are open, the inboard outlets of the first group of upright passageways are closed, the outboard outlets of the second group of upright passageways are closed, and the inboard outlets of the second group of upright passageways are open while the fans operate in the clockwise mode. In contrast, the outboard outlets of the first group of upright passageways are closed, the inboard outlets of the first group of upright passageways are open, the outboard outlets of the second group of upright passageways are open, and the in board outlets of the second group of upright passageways are closed while the fans operate in the counterclockwise mode.
These and other aspects of the present invention are advantageous because they each pertain to the efficient operation and/or timely operation of kiln systems. In particular, the kiln system of the present invention permits heated air to be selectively injected into the recirculating flow path such that the heated air can be injected on the high-pressure sides of the air moving devices in a manner that facilitates mixing of the heated air with the circulating air without introducing substantial impedance into the recirculating flow path, and most preferably the heated air is injected in a manner that advantageously enhances flow along the flow path.